Lipid micellar particles in the form of vesicles, also known as liposomes, are known and may be produced in the laboratory through the formation of a lipid film by the rotary evaporation of an organic solvent, followed by the hydration of the lipid film using methods of sonication, dialysis, injection or reverse phase evaporation to form the liposomes.
Such laboratory methods have been difficult to adapt to produce liposomes in commerical quantities. Generally, the lipid film or powder is formed in a first step, for example by spray drying the lipid, and then this film is hydrated in a separate apparatus. For example, an advantageous method for producing significant quantities of small unilamellar vesicles by the hydration of a dried lipid film in a modified homogenizing device is described in U.S. Pat. No. 4,753,788. However, existing methods for the manufacture of liposomes do not provide for the formation and vesiculization of lipid films in a single container, which would provide significant advantages in the production of liposomes, particularly multilamellar vesicles (MLVs), in a sterile environment. Such a method would be advantageous in that MLVs cannot be sterilized by filtration or heat sterilization for pharmaceutical use. In addition, existing art does not provide a method for the effective large scale, single vessel production of liposomes which contain an amphiphilic or lipophilic (i.e., hydrophobic) therapeutic agent which must be dissolved in the lipid film, and the transfer of a drug-containing lipid film from an evaporation vessel to a hydration vessel can involve significant problems.
Accordingly, it has been a desideratum to provide an apparatus and method for both the establishment and hydration of a lipid film to form liposomes in a single vessel in quantities and under conditions which are adaptable to commercial production.
The invention may be briefly summarized as method and apparatus for the vesiculization of an amphiphilic lipid material in an aqueous phase, comprising the use of a modified thin-film evaporator for both the film-forming and lipid hydration steps of liposome formation. More particularly, the invention includes a method for the formation of liposomes, preferably multilamellar vesicles, comprising the steps of introducing a mixture including amphiphilic lipid material (preferably including an amphiphilic or lipophilic biologically active agent) and a liquid into a closed chamber having a cylindrical interior wall, a rotatable shaft disposed coaxially with respect to the wall and having at least one rotor blade secured thereto and extending radially therefrom into a spaced, film-forming relationship with the wall; forming a film of the lipid material on the wall by rotation of the blade and evaporation of the liquid; introducing an aqueous phase into the chamber; and hydrating the film by rotating the blade at a speed which is sufficient to form liposomes.
Preferably, the lipid film is of uniform thickness and essentially all of the liquid which has been introduced into the closed chamber during the film-forming process is evaporated prior to the introduction of the aqueous phase into the chamber.
The method of the invention provides for the use of the described apparatus wherein the film-forming zone between the rotor blade(s) and the wall is of uniform thickness, that is, the zone is free of variations in thickness which produce incomplete or uneven drying of the lipid mixture; and in particular is free of depressions in the wall portion adjacent the rotor blade. The apparatus includes a fluid feed inlet and a fluid outlet in fluid communication with the chamber, each being disposed in a manner which continues the uniform thickness of the film-forming zone. For example, neither the inlet or outlet openings are positioned radially adjacent the rotor blades within the zone. Preferably, the fluid outlet is disposed either in an end of the closed chamber outside of the film-forming zone, or comprises a valve which provides a planar surface which is flush with the surface of the closed chamber to maintain such uniform thickness.
Other aspects of the invention will become clear from a reading of the following detailed description of the invention.